Ionic-current jumps caused by the activation of individual transmembrane molecular channels are recorded using the external patch electrode technique. Unit conductances and gating kinetics are studied in the postsynaptic membranes of cultured rat, human and chick muscle and also in mouse spinal cord neurons. Gating kinetics are determined for various agonists and partial agonists, as cells undergo developmental change or are changed by altered membrane lipid environment. Electron spin resonance and fluorescence measurements are done on acetylcholine-receptor protein isolated from electroplax in order to devlop a molecular probe for the conformation changes induced by agonists.